It has long been recognized that when transmitting signals to a remote receiver that characteristics of the relevant transmission medium can affect the quality of the received signals. Cable or wire transmission lines share a number of characteristics. These include signal distortion caused by external noise sources, varying electrical characteristics of the medium due to inconsistent quality and impedance miss-matches due to connections to the medium.
It has also been shown that many communication problems are not related to the baud rate but rather to the slew rate of the transmitted signals. A high rate of transition in the waveform voltage from one level to another (or high slew rate) may contribute to a high communication rate. However, this mode of operation will electrically couple into other adjacent wiring and create "crosstalk", cause excessive signal oscillations (ringing), or otherwise distort the waveform. A low slew rate will slow down the communication rate, minimizing these problems, but result in a longer time to complete messages.
One known approach requires the use of high quality, expensive, coaxial cable. Such cable provides substantially constant impedances, irrespective of length when properly terminated. However, coaxial cable is not a viable solution in many systems. It is expensive and because it is shielded can be inconvenient for field installers and maintenance personnel. While possibly usable in many new systems it is not a cost-effective replacement for existing media.
There is a continuing need for improved transmission systems which address at least some of the above enumerated problems. Such improvements are especially important given the continuing trend to distributed, multi-processor systems.
Preferably such systems will provide increased degrees of communication reliability with a variety of transmission media. In addition, it would be desirable if such improvements could be achieved without a need for extensive and expensive upgrades to existing transmission systems.
Thus, there is a continuing need for distortion minimizing systems which can automatically respond to different transmission media and to exterior noise sources.